In a conventional electric motor control system, a plurality of electric motor control devices respectively provided for a plurality of electric motors and an upper-level control device that controls the electric motor control devices are connected to each other via a network. As a command communication system between the upper-level control device and the electric motor control device in such an electric motor control device, a technique has been known in which a positioning command is transmitted from the upper-level control device to the electric motor control device at the first step, a start command is transmitted from the upper-level control device to the electric motor control device at the second step, and upon receiving the start command, the electric motor control device drives the electric motor (see, for example, Patent Literature 1).
As another command communication system between the upper-level control device and the electric motor control device, for example, a technique has been known in which a sequential command is transmitted from the upper-level control device to the electric motor control device for each control cycle to drive the electric motor (see, for example, Patent Literature 2).